Bundaberg Regional Council East Sewerage Treatment Plant Regional Sewerage Pump ...€¦ · ·...

Regional Sewerage Pump Station - Design Report

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Bundaberg Regional Council

East Sewerage Treatment Plant

Regional Sewerage Pump Station

Design Report

Revision 1

December 2011


Page II

Document Control

Version Date Author Reviewer

Name Initials Name Initials

1 January 2012 Megan Kraft MK Kane Macready


Page III

Contents

EXECUTIVE SUMMARY ........................................................................................................................... 1

1 INTRODUCTION ............................................................................................................................ 3

2 SEWERAGE LOAD .......................................................................................................................... 4

3 RISING MAIN DESIGN .................................................................................................................... 6

3.1 ALIGNMENT .......................................................................................................................................................... 6

3.2 SIZE AND MATERIAL ................................................................................................................................................ 6

3.3 CONSTRUCTABILITY ................................................................................................................................................. 9

3.4 DESIGN SPECIFICATION ............................................................................................................................................ 9

4 SEWERAGE PUMP STATION DESIGN ............................................................................................ 10

4.1 SITE AND LAYOUT ................................................................................................................................................. 10

4.2 DESIGN LIFE OF SEWERAGE PUMP STATION COMPONENTS ........................................................................................... 10

4.3 PUMPING SYSTEM ................................................................................................................................................ 11

4.3.1 Submersible Pumps ..................................................................................................................................... 11

4.3.2 Dry Mounted Self Prime Pumps. ................................................................................................................. 12

4.4 INLET MANHOLE .................................................................................................................................................. 12

4.4.1 Size and Layout ........................................................................................................................................... 12

4.5 WET-WELL DESIGN .............................................................................................................................................. 12

4.5.1 Layout ......................................................................................................................................................... 13

4.5.2 Pump Control Volume and Pump Starts ...................................................................................................... 13

4.5.3 Size .............................................................................................................................................................. 14

4.5.4 Control Levels .............................................................................................................................................. 14

4.5.5 Benching ..................................................................................................................................................... 14

4.6 EMERGENCY STORAGE .......................................................................................................................................... 15

4.7 EMERGENCY RELIEF SYSTEM ................................................................................................................................... 16

4.8 POWER SYSTEM ................................................................................................................................................... 16

4.9 CONTROL AND TELEMETRY SYSTEM.......................................................................................................................... 16

4.10 OPERATIONAL ISSUES ............................................................................................................................................ 16

4.10.1 Standby Generator ................................................................................................................................. 16

4.10.2 Standby diesel pump............................................................................................................................... 17

5 ESTIMATE OF COST ..................................................................................................................... 18

6 ODOUR MANAGEMENT .............................................................................................................. 18

7 SAFETY IN DESIGN ...................................................................................................................... 20

8 CONCLUSIONS AND RECOMMENDATIONS ................................................................................... 21

8.1 RISING MAIN....................................................................................................................................................... 21

8.2 SEWERAGE PUMP STATION .................................................................................................................................... 21

8.3 ODOUR CONTROL ................................................................................................................................................ 22


Page 1 of 22

EXECUTIVE SUMMARY

SITUATION – Bundaberg Regional Council (BRC) has identified the need for a new regional sewerage

treatment plant (STP) to provide for population growth in East Bundaberg and the communities between

Burnett Heads and Elliot Heads. The proposed regional STP will be located in Rubyanna and will replace the

ageing East Sewerage Treatment Plant (ESTP) on Alexandra Street.

It is proposed that existing flows to ESTP will be diverted to the new regional plant at Rubyanna by a

regional pump station located at the ESTP site and associated rising main.

ISSUES – Sewerage flows currently are delivered to the ESTP by a number of pump stations and rising

mains. In order to divert flows from ESTP to the proposed treatment plant at Rubyanna, sewerage will be

required to be diverted from the inlet works of ESTP to the proposed pump station. Note that the pump

station will have to be incorporated with valving that will allow the incoming sewer mains to feed either the

pump station or the old treatment plant during the commissioning process.

It has also been advised that the existing ESTP currently experiences odour issues at the inlet works. As part

of this report an investigation into the available odour treatment systems has been completed and

recommendations made.

SOLUTION – A preliminary design has been completed as per WSA-04 Sewerage Pumping Station Code for

the rising main and sewerage pump station. The specification for each is detailed in the tables below.

Preliminary drawings for the pump station layout are included in Appendix A and a preliminary long section

of the rising main has been completed (Appendix C). The preliminary estimate of cost for the construction

of the rising main and pump station is $9,545,735 excl GST.

Sewerage Rising Main Specification

Pipe Diameter 600mm

Pipe Material Glass Reinforced Plastic (GRP)

Jointing Mechanism Socket-Spigot

Allowable Joint Deflection As per manufacturers tolerance

Minimum Pipeline Cover 900mm

Alignment from Property Boundary As per preliminary design drawings


Page 2 of 22

Sewerage Pump Station Specification

Inlet Manhole 3.0m diameter

Wet Well Connection 2 x 525mm diameter @ 2%

Wet Well Diameter 8.0m split well

Control Levels As per Table 7 and Appendix A

Pumps Duty/Standby submerged fixed speed or variable speed

pumps. Pump duty’s:

Initial Duty – 492 L/s @ 19.3m

Interim Duty (2036) – 603 L/s @ 25.8m

Ultimate Duty – 703 L/s @ 32.6m

Emergency Storage Minimum 2.02 ML (Existing oxidation ditch)

As odour is currently an issue at the East SPS it is recommended that the following odour control systems

are put in place:

Chemical Dosing (Ferric Chloride) of the pump stations upstream of this proposed pump station;

Well washing systems be installed in all pump stations; and

A bio filter odour control unit installed at the proposed sewer pump station.


Page 3 of 22

1 Introduction

Bundaberg Regional Council (BRC) has identified the need for a new regional sewerage treatment plant to

provide for population growth in East Bundaberg and the communities between Burnett Heads and Elliot

Heads. The proposed regional STP will be located in Rubyanna and will replace the ageing East Sewerage

Treatment Plant (ESTP) on Alexandra Street.

It is proposed that existing flows to ESTP will be diverted to the new regional plant at Rubyanna by a

regional pump station located at the ESTP site. Macready and Associates have been commissioned by BRC

to complete a design report for the proposed pump station.

This report will address the following key items:

Current and future sewerage load;

Layout of sewerage pump station;

Size the pump station structure for current and future loads;

Size pumping equipment for current and future loads;

Recommend an emergency storage solution;

Strategy for redundancy of operation;

Odour management; and

Rising main size and alignment.


Page 4 of 22

2 Sewerage Load

The ESTP services approximately 35,000EP within the eastern area of Bundaberg City. The catchment is

serviced by a number of sewerage pump stations that deliver flows to the ESTP inlet works. The pump

stations within the catchment are summarised in Table 1 and shown in Figure 1.

Table 1 – ESTP Pump Stations

Sewerage Pump Station Address

SPS1 Orr Street

SPS7 Alexandra Street

SPS15 Reddan Street

SPS20 Queen Street

SPS28 Hartnell Street

Figure 1 – East STP Pump Station Layout

The ESTP catchment is primarily made up of residential, commercial and industrial facilities. The catchment

is well developed and includes the Bundaberg CBD.

The Bundaberg Sewerage Planning Report (Cardno, 2008) details the expected sewerage flows to ESTP to

the ultimate scenario. The projected sewerage flows are summarised in Table 2.


Page 5 of 22

Table 2 – ESTP Sewerage Loads

East STP 2011 2016 2021 2026 2036 2056 Ult

EP 35083 37025 39291 41170 43100 46802 54812

ADWF (ML/d) 7.72 8.15 8.64 9.06 9.48 10.30 12.06

ADWF (L/s) 89 94 100 105 110 119 140

PWWF (L/s) 492 519 550 577 603 656 703 * Based on the Bundaberg Sewerage Planning Report, Cardno 2008

The planning report also analysed the sewerage pump stations to determine their capacities and required

upgrades over the planning horizon. The details of the contributing sewerage pump stations and

associated upgrades are summarised below (Table 3):

Table 3 – East STP Pump Stations

Pump Station 2011 2016 Ult Note

SPS1 41 43 75.9 2016 pump upgrade required

SPS7 124 128 143.6 Nil

SPS15 216 217 218.6 Nil

SPS20 59 61 74 Nil

SPS28 52 70 190.6 2015 pump upgrade required

TOTAL 492 L/s 519 L/s 703 L/s * Based on the Bundaberg Sewerage Planning Report, Cardno 2008

The ultimate sewerage load for the catchment is 703L/s. Section 4 details the pump station infrastructure

design to cater for the current and ultimate flows using a staged approach.


Page 6 of 22

3 Rising Main Design

3.1 Alignment

The alignment of the rising main from the proposed sewer pump station to RSTP has been agreed with BRC

and is shown in Figure 2. The alignment follows existing road reserves and private property boundaries to

Rubyanna STP. The preliminary design is displayed in Appendix C.

Figure 2 – Rising Main Alignment

3.2 Size and Material

The size of the rising main is based on the pumping rate, detention time and head loss.

To ensure that the results could be interpreted clearly, three flows were chosen to calculate system

requirements. These were:

1. 2011 – Present;

2. 2036 – Intermediate (To coincide with the design life of the pumps and electrical equipment of 25

years); and

3. Ultimate.

System curves were calculated based on various nominal pipe diameters (DN450, DN500 and DN600) to

evaluate the performance. A combined rising main, consisting of a DN500 for initial flows and a DN450 in

parallel for future flows was also considered. The results are shown in Figure 3.


Page 7 of 22

Figure 3 – Mains Size Comparison

The results indicate that the minimum head system is from the two smaller mains operating in parallel.

However, the indicated operational savings are less than 10% which is far outweighed by the increased

capital cost. The only other solution that meets WSA-04 requirements with respect to recommended

velocities over the range of flows is the DN600 main. The velocity range to comply with WSA-04

recommendations and general practice, is that a minimum of 1.5 m/sec is required and a maximum of 3.0

to 3.5 m/sec.

Further calculations have been carried out to determine the appropriate material for the rising main. We

have analysed Ductile Iron Cement Lined (DICL) and Glass Reinforced Plastic (GRP). High Density

Polyethylene (HDPE) has not been included in this analysis due to concerns regarding de-rating for fatigue,

which could be a concern in a sewage pump station. Also, to achieve the required pressure rating the wall

thickness is quite large. Installation (welding) requires specialised rigs for pipes this size and this is also a

concern for maintenance and future cut-ins if required. The results are given in Figure 4.


Page 8 of 22

Figure 4 – Mains Type Comparison

The results indicate that the DN600 GRP pipe is the most economical option in terms of operational costs,

with the DN600 DICL incurring approximately 17% increase and the DN525 GRP incurring approximately

65% increase in operational (power) costs. Based on current ADWF and a power cost of $0.15/KWh, the

annual power costs are around $30,000/year at ADWF flows.

Based on budget costs from suppliers, the GRP is also the lower capital expenditure when compared to the

DICL, making it the preferred pipe material. The capital savings on the DN525 GRP would not be sufficient

to justify the additional operational costs - approximately $300,000 in capital savings against approximately

$487,000 in power costs over 25 years (today’s costs).

The recommended maximum detention time within rising mains is 2 hours (WSA-04). The detention time in

the rising main is 5.3 hours for initial flows and 3.3 hours for the ultimate flows. This is greater than the

recommended times and will lead to consequent septicity in the mains and potential odour concerns, as

well as the potential for corrosion of structures including concrete pipe lining. Given that GRP does not

have a cement lining and is constructed using inert materials then it will fair best under these

circumstances. As the rising main will also be constructed within a marine area GRP will provide greater

resistance to corrosion from external factors.

Air relief valves should be installed on all high points in the mains to minimise the possibility of air

entrainment. Scour valves should also be included on low points in accordance with WSA standard

drawings.

Technical data on glass reinforced pipe is included in Appendix D.


Page 9 of 22

3.3 Constructability

The alignment of this main is proposed to be predominantly constructed in open space/BRC road reserve

which is expected to result in a relatively straight forward construction phase due to the minimal works

requiring traffic control and the need to provide access to businesses or residents.

BRC have indicated that the proposed Rubyanna STP site is above the 100 year ARI flood level and that no

major earthworks will be required to lift the level of the site. Given this we have designed the rising main

and pump station based on the existing natural surface level.

3.4 Design specification

The following design specification (Table 4) should be utilised for the detailed design of the rising main for

the project. A preliminary long section has been completed using contour levels from GIS data (Refer

drawings 11026-01 to 11026-41). During the detailed design phase, engineering survey of the alignment

will be required and services potholed to ensure clashes are avoided.

Table 4 – Sewerage Rising Main Specification

Pipe Diameter 600mm



Allowable Joint Deflection As per manufacturers recommendation

Meters Flow meters to be install and start and end of main




Page 10 of 22

4 Sewerage Pump Station Design

4.1 Site and Layout

The proposed regional pump station will be located within the existing ESTP site as shown in Figure 5. The

site was chosen due to availability of space and minimal construction costs to divert existing flows from the

inlet works of ESTP to the pump station.

The preliminary of the pump station is detailed in Appendix A.

Figure 5 – Proposed Regional Pump Station Location

4.2 Design Life of Sewerage Pump Station Components

Buried sewer pump station assets shall be designed for a nominal asset life of at least 100 years, with other

components requiring earlier renovation or replacement. Typical designated asset lives for sewer pump

station systems are shown in Table 5 as per WSA-04.

Table 5 – Sewer Infrastructure Design Life

Item

Sewers, pressure

mains, civil structures

(wet-well, emergency

storage and ancillary

structures)

Valves Electrical

Equipment Pumps Pipework

Wet-well

appurtena

nces

Instrumentation,

SCADA and

control devices

Minimum

Design Life 100 30 25 25 50 20 15


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4.3 Pumping System

Selection of the preferred rising mains as DN600 GRP results in the following pump duties (final head to be

dependent on final pump station design):


Interim Duty (2036) – 603 L/s @ 25.8m


Options considered for the pumps include:

Duty/standby configuration submersible pumps; and

Above ground self-priming pumps.

4.3.1 Submersible Pumps

Major pump manufacturers can provide submersible pumps that are capable of achieving the ultimate

pump duty. The ultimate pump duty can be achieved with fixed speed pumps with appropriate impeller

changes to meet the required duties.

The design life of the pumps (and electrical switchboards) is nominally 25 years; therefore if flows as

predicted eventuate then pumps and switchboards will need to be replaced before ultimate flows are

achieved. It is recommended that the pump station civil structure and pipework be designed for ultimate

flows, but that mechanical and electrical equipment be designed for interim flows (i.e. 2036).

Consequently, the initial design pump duties would be:


Interim Duty (2036) – 603 L/s @ 25.8m

The upgrade from initial duty to interim duty can be achieved with impeller changes, or with the use of

variable speed drive units. The mains velocity at the initial duty is 1.55 m/s and 1.90 m/s at the Interim

duty.

By using variable frequency drives, flow velocity can decrease to around 0.9 – 1.0 m/s (or lower) providing

that the higher velocities are attained on a regular basis to prevent settling in the mains. The scouring

velocity will be achieved at a flow of approximately 300 L/s and can easily be achieved with a variable

speed drive unit.

The variable speed drive unit would also provide a more even flow into the treatment plant, which may be

advantageous to the treatment process (dependent on treatment process selected).

Typically, this would result in fixed speed pumping of around 5 hours per day at ADWF to variable speed

pumping of 10 – 12 hours per day. Other advantages of using variable speed drives include the reduction in

surges and water hammer due to controlled starting and stopping of the pumps. For a 300kW pump

controller the additional costs are $25,000 - $30,000 per unit.


Page 12 of 22

4.3.2 Dry Mounted Self Prime Pumps.

Dry mounted self-prime pumps are becoming more common for use in sewage pump stations, and for this

project four dry mounted Gorman Rupp self-priming pumps would be required plus standby units. This

would require a much larger footprint than the submersible option, and would also lead to NPSH concerns

when operating at the lower levels that are required for the emergency storage. Operation of the pumps

cannot be staged with respect to inlet flows as there must be sufficient flow to achieve adequate velocities

in the rising mains, therefore negating some of the advantages of using multiple pumps.

The advantages of the surface mounted self-priming pumps (predominantly maintenance access) are not

considered sufficient to justify further consideration of this option at this stage.

4.4 Inlet Manhole

The inlet manhole will act as the receiving manhole to collect all flows currently discharging to the ESTP

inlet works. The inlet manhole is to be located within the pump station site.

The inlet MH shall fulfil the following functions:

a) Collect all sewage flows draining to the station.

b) Unless approved otherwise, form part of an emergency relief system that enables retention of

gross solids/trash, scum and gas within the sewer system (Refer to Clause 5.6.4).

c) House overflow monitoring/telemetry equipment.

d) Provide an emergency wet-well for by-pass pumping in the event of a station failure.

4.4.1 Size and Layout

The inlet manhole will be receiving flows from two existing rising mains of diameter 375mm and 600mm.

These rising mains are currently delivering flows from the catchment to the inlet works of ESTP. To

accommodate the inlet of these rising mains and outlets to the pump wet well and emergency storage a

3m diameter inlet manhole is recommended. The size of the inlet manhole should be confirmed during

final design taking into account the aperture required of the two rising mains, gravity connection to wet

well and overflow pipes.

4.5 Wet-Well Design

Due to the large volume of flows through the pump station in accordance with WSA-04 either two wet

wells or a divided wet well are required to ensure service with one wet well not in operation.

The wet-well shall be arranged taking into account the need to:

a) extend the sump below the level of the incoming sewers;

b) be able to isolate, empty and clean the wet-well;

c) avoid “dead zones” where solids can accumulate;

d) avoid discharge from the inlet pipe directly onto a pump;

e) allow adequate clearance between the base and sides of the wet-well and pump inlets;

f) avoid generation of septic sewage;

g) reduce H2S gas generation by ensuring that flow from inlet pipe minimises turbulence on discharge

into wet-well; and

h) Pump manufacturer’s design and installation recommendations.


Page 13 of 22

The design shall incorporate either a drop pipe from the inlet isolating valve at the end of a horizontal inlet

pipe or a steeply-sloped inlet pipe with an isolating valve in the wet-well. In either case, the inlet pipe shall

end at least one pipe diameter above the normal pump cut-out level to allow the inlet pipe to drain

completely on every pump cycle.

The depth of the wet-well shall be determined having regard to:

i. sewer invert;

ii. cut-in/cut-out volume;

iii. minimum pump submergence; and

iv. minimum depth below the pump intake specified by the pump manufacturer.

4.5.1 Layout

For large pump stations WSA-04 specifies that either two separate wet wells or a split wet well is required.

For the proposed pump station it is recommended that a split well is constructed. A split well has the

following advantages:

Reduced construction costs; and

Ability to shut down one side of well for maintenance or if pumps fail.

Within the split well a connection between the two compartments will be required with a valve to enable

isolation.

Flows from the inlet manhole to the pump well will be via two gravity mains entering the two

compartments of the wet well; each of these mains shall have an isolation valve located within the inlet

manhole to enable isolation of either compartment of the wet well. Appendix A shows the proposed layout

of the wet well and connection to the inlet manhole.

4.5.2 Pump Control Volume and Pump Starts

The pump control volume is based on the following calculation:

Where

Vww is the pump control volume (cut-in / cut-out volume)

Qp is the pumping rate

Smax is the maximum allowable number of pump starts per hour

This volume ensures that for any ratio of dry weather inflow to the wet well and pumping rate the

maximum allowable number of starts is not exceeded.

The maximum allowable number of pump starts per hour shall be 8 or 90% of manufacturer’s

recommended number, whichever is lower, subject to power supply and equipment limitations.

Table 6 summarises the pump control volumes for all three flow stages considered (2011, 2036 and

ultimate) assuming a maximum number of starts per hour of 8.


Page 14 of 22

Table 6 – Pump Control Volume

Year Flow (L/s) Vww (kL)

2011 492 55.4

2036 603 67.85

Ultimate 703 79.1

4.5.3 Size

For the ultimate flow the pump control volume for the pump station is 79.1kL. An assessment of the pump

operating depth has been completed for a number of wet well diameters. The diameter of the wet well will

affect the depth of the pump station, although larger diameter wells have an increased cost. Table 7 shows

the pump operation depths for the proposed wet well and corresponding overall depth for the pump

station.

Table 7 – Wet Well Diameters and Operating Depths

Wet Well Diameter Pump operating depth Overall wet well depth

5.5m 3.33m 6.909m

6.0m 2.80m 6.377m

6.5m 2.38m 5.963m

7.0m 2.06m 5.635m

8.0m 1.57m 5.353m

As the ground conditions of the proposed pump station site are not known we have assumed a pump well

diameter of 8.0m for the preliminary design. Depending on the results of geotechnical investigations it may

be more economical for a smaller diameter wet well with a greater depth. This should be confirmed

during final design.

4.5.4 Control Levels

Control levels are set in WSA-04 as per Table 8. Control levels for the pump station are also shown in Table

8 based on a 8.0m diameter wet well and an inlet to the wet well of 7.365m AHD.

Table 8 – Control Levels

Control Level (m AHD) Description

Duty pump cut out 5.642 set in accordance with the heights corresponding to the cut-

in/cut-out volumes and being not lower than the minimum

submergence level of the pumps

Duty pump cut in 7.215 set at least 150 mm below the incoming sewer invert level

Standby pump cut in 7.365 set at least 150 mm above the duty cut-in level

4.5.5 Benching

The wet-well base shall be designed with benching to provide self-cleansing properties, while also guiding

sewage flow into the suction of the pumps. The self-cleansing benching shall extend such that there are no

dead areas where grit can accumulate or settlement can occur.

The inlet sewer shall discharge at a height above the floor that ensures adequate flow to the pump

intake(s).


Page 15 of 22

4.6 Emergency Storage

Emergency storage will be provided in order to provide adequate time for operations and maintenance, as

well as catering for flows greater than the design capacity of the sewerage pump station (subject to license

conditions). The volume of storage required to be provided is equal to four hours of ADWF, for the

ultimate case the required emergency storage is 2.02 ML.

Within the existing ESTP there is an oxidation tank located adjacent to the proposed SPS site. BRC have

indicated they would like to utilise this tank as emergency storage for the pump station. The existing

oxidation tank is currently uncovered, for effective management of stormwater a roof should be installed

over the structure.

The floor level of the oxidation tank is at RL8.615, the top water level at RL12.14 with an area of 1,313m2.

The total volume of the tank is 4.63ML. To achieve the required storage the overflow from the pump

station to the existing stormwater system will need to be set a minimum level of 10.155m. To utilise the

maximum amount of storage within the oxidation tank it is recommended an overflow level of 11.75m is

used.

It is recommended that the inlet manhole and wet well surface level is set a 12.14m with appropriate filling.

This will ensure there is additional emergency storage above the minimum required by WSA-04.

Figure 6 shows the proposed emergency storage arrangement.

Figure 6 – Emergency Storage Arrangement


Page 16 of 22

4.7 Emergency Relief System

Pumping stations require an emergency relief system (ERS) to be provided from the inlet manhole or

emergency storage. The ERS can discharge to the following systems (in order of preference):

An adjacent sewer catchment.

A formed stormwater drain e.g. pipe, channel etc.

An unformed drain, creek or watercourse.

A harbour or river.

Tidal waters

The closest available outlet is the existing outfall from ESTP into the Burnett River. The location of the

emergency relief overflow is to be confirmed during final design.

4.8 Power System

As the proposed site is an existing sewerage treatment plant it is assumed that there will be adequate

power supply infrastructure to the site. As the pump station will be required to be operational for a period

of time whilst the ESTP is still operational there may be some need to upgrade the internal power supply

infrastructure. A temporary power connection may also be required during commissioning of the pump

station.

4.9 Control and Telemetry System

All control systems shall be compatible with existing systems, terminology and processes used by BRC.

These shall include but not be limited to:

a) Pumping control;

b) Alarms; and

c) Telemetry system.

The telemetry system shall be capable of connection to BRC’s existing telemetering system.

4.10 Operational Issues

The pump station is designed with duty & standby pumps. An additional spare pump could be kept in the

store to ensure that during pump maintenance (where pump removal is required) that 100% standby

capacity is available at all times. This requirement is not as relevant where the emergency provision is a

standby diesel pump.

4.10.1 Standby Generator

For an ultimate single pump sizing of 310kW starting with a variable speed a 400-500 kVA (to be confirmed

during final design) generator set would be required to supply power to the pumps during power outages.

Should operation with both pumps in parallel be required a generator set of around 800kVA would be

required. The switchboard should be designed with an Automatic Transfer Switch (ATS) for automatic

operation.


Page 17 of 22

4.10.2 Standby diesel pump

A standby diesel pump can be installed, capable of the ultimate PWWF at maximum speed. Speed would be

limited initially to match the current or interim flows. The diesel pump would provide the following

advantages;

No switchboard so can be used for switchboard outages as well as power outages.

Speed can be varied to suit flows.

Diesel sizing does not have to take into consideration motor starting currents (not relevant when

VSD used).

Switchboard could have ATS installed so that diesel generating set can be readily installed if

required, although this would be unlikely.


Page 18 of 22

5 Estimate of Cost

A preliminary estimate of cost has been completed for the project as detailed in Table 9.

Table 9 – Preliminary Estimate of Cost

Item Quantity Unit Price Amount

Rising Main (600dia GRP) 5000m $1,550/m $7,750,000

Sewer Pump Station Civil 1 $839,300 $839,300

Pump station pipework and equipment 1 $59,730 $59,730

Pump station pumps 1 $38,900 $38,900

Pump station electrical and telemetry 1 $57,805 $57,805

Emergency Storage Roof*1 1 $300,000 $300,000

Planning, Design and Project Management*2 1 $255,000 $255,000

Contingency 20% $1,860,147

Total (excl GST) $9,300,735

*1 Based on 18m x 100 portal frame shed. Alternative methods of coverage should be investigated in final

design.

*2 Based on a design rate of rising main of $25,000/km and SPS Design Rate of $50,000. Including a project

management cost of $4,000/week with a 20 week construction program.

6 Odour Management

It has been identified that the management of odour is a significant issue that will need to be addressed

during the design of the pump station and rising main. Sewerage odour is caused by the decomposition of

sewerage, forming gases which may include Hydrogen Sulfide, Ammonia, Methane, Carbon Dioxide, Sulfur

Dioxide and Nitrogen Oxides. The most common type of gas is Hydrogen Sulfide (H2S).

Almost all odour generation issues in municipal sewerage are dependent on detention time within the

sewerage collection system. A number of variables can affect the rate at which H2S is generated, these

include:

Anaerobic conditions in the form of rising main lengths can increase the rate of generation of

odour;

Effects of demand management which results in lower flows and higher concentration of Chemical

Oxygen Demand (COD), Sulfates and other pollutants. This would lead to longer detentions in the

collection system; and

Trade waste component within the catchment which can lead to higher concentrations and rates of

generation of H2S.

Odour control systems generally fall into two categories; chemical treatment and biological treatment. Manipulation of conditions to prevent the reduction of sulphates (addition of O2, NO3, H2O2), addition of chemicals that react with the H2S to prevent the release of the gaseous form (eg. ferric sulphate), and increasing the pH to alter the chemical equilibrium and hence reduce release of H2S (eg. using NaOH or Mg(OH)2) are examples of chemical approaches).

http://en.wikipedia.org/wiki/Hydrogen_sulfide

http://en.wikipedia.org/wiki/Ammonia

http://en.wikipedia.org/wiki/Methane

http://en.wikipedia.org/wiki/Carbon_dioxide

http://en.wikipedia.org/wiki/Sulfur_dioxide

http://en.wikipedia.org/wiki/Sulfur_dioxide

http://en.wikipedia.org/wiki/Nitrogen_oxides


Page 19 of 22

Biological treatment includes addition of selected strains of bacteria, addition of nutrients to promote growth of certain bacteria, and the removal of biofilms from the pipe walls which contain the sulphate reducing bacteria. It is common practice within the reticulation system to favour chemical treatment.

Historical records have indicated a number of odour complaints in the area surround ESTP and has been

identified by BRC to be an issue that needs to be addressed.

WSA-04 has identified a number of management techniques that can be implemented in the design phase,

these include:

Installation of benching to ensure free flowing of sewerage in the well and no dead areas where

solids can accumulate;

Installation of wet well washers to reduce the frequency of wet well cleaning and the formation of

H2S. These wet well washers should be connected to the water reticulation system with a

disinfectant that will reduce bacterial activity and put H2S back into solution;

Rising main design to minimise detention time to be less than 2hours;

Installation of educt and induct ventilation as per standard drawings SEW 1407 and 1408, is some

cases mechanical means of educt and induct may reduce the hazard of toxic gases. In this case,

mechanical means can be retrofitted to any existing ventilation system.

As odour issues are already being experienced at the inlet of ESTP then it is inherent that the proposed

sewerage pump station and 5km rising main will produce more odour at the inlet of Rubyanna STP.

The recommended maximum detention time within rising mains is 2 hours (WSA-04). The detention time in

the rising main is 5.3 hours for initial flows and 3.3 hours for the ultimate flows. This is greater than the

recommended times and will lead to consequent septicity in the mains and potential odour concerns at the

treatment plant inlet works. This is also discounting any effect in the mains leading into this pump station.

Based on this it is recommend that the following odour control systems are installed:

Chemical Dosing of the pump stations upstream of this proposed pump station. Ferric Chloride is

currently used in the existing pump station within the catchment.

Well washing systems be installed in all pump stations.

Because chemical dosing does not remove all odour producing components an odour control unit

should be installed at the new pump station. A bio filter odour control unit would remove the

majority of odour causing compounds, and generally requires less maintenance than an activated

carbon filter. As this is currently an industrial area this may provide sufficient control. In a more

intensive residential area a final activated carbon scrubber unit may be required. A typical odour

control unit detail is shown in Figure 7.


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Figure 7 – Odour Control Unit

7 Safety in Design

A risk assessment for the project is included in Appendix B. This assessment addresses potential risks

associated with construction, operation and maintenance of the project.


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8 Conclusions and Recommendations

This report details the preliminary design of a proposed regional pump station at ESTP and rising main. The

proposed pump station will divert flows from the existing sewerage treatment plant to the proposed plant

at Rubyanna. The proposed sewerage pump station will ultimately receive flows of 703L/s.

The preliminary estimate of cost for the construction of the rising main and pump station is $9,545,735 excl

GST.

8.1 Rising Main

A 600mm diameter GRP rising main shall transport flows from the proposed pump station to the new

Rubyanna STP. Table 10 below details the specification for the proposed rising main. The rising main

alignment shall follow exiting road reserves and property boundaries from ESTP to Rubyanna STP and the

alignment is shown in Figure 2.

A preliminary long section has been completed using contour levels from GIS data (Appendix C). During the

detailed design phase, an engineering survey of the alignment will be required.

Table 10 – Sewerage Rising Main Specification

Pipe Diameter 600mm



Allowable Joint Deflection As per manufacturers recommendations



8.2 Sewerage Pump Station

Preliminary design of the proposed sewerage pump station has been completed (Appendix A). Table 11

specifies the preliminary design parameters for the pump station. Preliminary design has been completed

in accordance with WSA-04 Sewerage Pump Station Code.

Table 11 – Sewerage Pump Station Preliminary Design Specification

Inlet Manhole 3.0m diameter

Wet Well Connection 2 x 525mm diameter @ 2%

Wet Well Diameter 8.0m split well

Control Levels As per Table 7 and Appendix A

Pumps Duty/Standby submerged fixed speed or variable speed

pumps. Pump duty’s:


Interim Duty (2036) – 603 L/s @ 25.8m


Emergency Storage Minimum 2.02 ML (Existing oxidation ditch)


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8.3 Odour Control

As odour is currently an issue at the East SPS it is recommended that the following odour control systems

are put in place:

Chemical Dosing (Ferric Chloride) of the pump stations upstream of this proposed pump station;

Well washing systems be installed in all pump stations; and

A bio filter odour control unit installed at the proposed sewer pump station.


Appendix A PRELIMINARY PUMP STATION DESIGN DRAWING


Appendix B Safety in Design


Risk matrix

Likelihood Severity

High

Fatality

Major illness

Long term disability

Medium

Injury/illness

Short term disability

Low

Minor injury/illness

High

Certain/nearly certain

H H M

Medium

Reasonably likely

H M L

Low

seldom

M L L

Project: BRC East Sewer Pump Station Design Stage: Preliminary Design

Version: 1 Date: 1/12/11 File: 10014

Phase Considerations Potential Hazards Risk Rating Mitigation options Action

L S R

Design for safe construction Open trench left overnight during

construction

Pedestrian trips and falls

Vehicle drives into trench

L M L Ensure trench is barricaded when Contractor not on site Specification and management of contract works

Materials stored on site become

unsecured

Climbing onto pipe and becoming

loose

Kids playing in sand and collapsing

L H M Ensure all materials are either stored off site or secure fencing

provided

Specification and management of contract works

Connecting into live sewer Infectious disease M M M Ensure all live connection is undertaken by Bundaberg Regional

Council or under their direction

Ensure inoculation

Ensure only qualified Plumbers and Drain Layers work on site

Damage to other services

Electrocution

L

H

M

Contractor to contact service authority to confirm and locate

underground services in vicinity of construction.

Consultation with service authorities to occur prior to construction.

DBYD service to be used. All services to be potholed prior to

construction.

Safe detour routes (Main St & Esplanade

closure)

Injury from vehicle conflict on detour

route.

L M L Traffic management according to MUTCD Considered further during construction

Tree root system damaged during

construction

Tree dies, falls onto road or verge

injuring driver or pedestrian

L H M Ensure vegetation protection works is provided at identified

locations.

Sewer alignment to minimise impact of root system.

Specification and management of contract works to ensure

vegetation protection works is implemented

Trench collapses during excavation

>6.5m

Construction worker buried alive L H M Ensure qualified contractor is employed and contract

specifications adhered to

Specification and management of contract works

Design to facilitate safe use Sewer manhole protrudes above ground

level

Pedestrian trips and falls L L L Ensure manhole is clearly visible

Ensure sewer manhole is set in the correct height in relation to

surrounding ground levels

Specification and management of contract works to ensure good

transition from ground to sewer manhole

Trench slumps Pedestrian trips and falls L L L Ensure trench is adequately compacted when backfilled Specification and management of contract works to ensure good

transition from ground to sewer manhole

Design for safe maintenance

Sewer manholes (all locations) Hurts back when removing manhole

lid

M M M Correct lifting posture, use manhole lifter All works on public sewer to be undertaken by


Falling in the manhole L M L Work in pairs All works on public sewer to be undertaken by


Service person hit by vehicle in

through traffic lane

L H M Final design to review location of manholes to

determine if any can be located in parking lanes or

verges.

Close off through lanes – MUTCD

Close off through lanes – MUTCD


Appendix C PRELIMINARY RISING MAIN DESIGN DRAWINGS


Page 5 of 2

Appendix D Promains GRP Specification

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